I used the following code to add and calculate field:-
gp.AddField_management(nn_file, "p_area", "DOUBLE", "", "", "", "", "NON_NULLABLE", "NON_REQUIRED", "")
gp.CalculateField_management(nn_file, "p_area", "[F_AREA]/1000", "PYTHON", "")
I keep getting error and couldn't figure it out..Any hint??? Thanks!